Chunk server: minor formatting fix.
Meta server: implement "delegate" rpc. The rpc allows to create and update the meta server access token and the key with the corresponding user id and given lifetime. The meta server configuration can be used to limit the max delegation token lifetime. The token and the key can be passed around via secure transport, or non secure transport, provided that the key is encrypted. Given the token and the key qfs client can "impersonate" the user that corresponds to the user id. One typical use would be for the actual "user" to authenticate using kerberos or x509 authentication with the meta server, and then create the delegation token and the key, then pass the token and the key to the services that need access to the file system as the user.